Intramolecular and Lateral Intermolecular Hole Transfer at the Sensitized TiO2 Interface

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• 作者：Ke Hu ; Kiyoshi C. D. Robson ; Evan E. Beauvilliers ; Eduardo Schott ; Ximena Zarate ; Ramiro Arratia-Perez ; Curtis P. Berlinguette ; Gerald J. Meyer
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：January 22, 2014
• 年：2014
• 卷：136
• 期：3
• 页码：1034-1046
• 全文大小：743K
• ISSN：1520-5126

文摘

Characterization of the redox properties of TiO₂ interfaces sensitized to visible light by a series of cyclometalated ruthenium polypyridyl compounds containing both a terpyridyl ligand with three carboxylic acid/carboxylate or methyl ester groups for surface binding and a tridentate cyclometalated ligand with a conjugated triarylamine (NAr₃) donor group is described. Spectroelectrochemical studies revealed non-Nernstian behavior with nonideality factors of 1.37 卤 0.08 for the Rup>III/IIp> couple and 1.15 卤 0.09 for the NAr₃p>鈥?/0p> couple. Pulsed light excitation of the sensitized thin films resulted in rapid excited-state injection (k_inj > 10p>8p> sp>鈥?p>) and in some cases hole transfer to NAr₃ [TiO₂(ep>鈥?/sup>)/Rup>IIIp>鈥揘Ar₃ 鈫?TiO₂(ep>鈥?/sup>)/Rup>IIp>鈥揘Ar₃p>鈥?p>]. The rate constants for charge recombination [TiO₂(ep>鈥?/sup>)/Rup>IIIp>鈥揘Ar₃ 鈫?TiO₂/Rup>IIp>鈥揘Ar₃ or TiO₂(ep>鈥?/sup>)/Rup>IIp>鈥揘Ar₃p>鈥?p> 鈫?TiO₂/Rup>IIp>鈥揘Ar₃] were insensitive to the identity of the cyclometalated compound, while the open-circuit photovoltage was significantly larger for the compound with the highest quantum yield for hole transfer, behavior attributed to a larger dipole moment change (螖渭 = 7.7 D). Visible-light excitation under conditions where the Rup>IIIp> centers were oxidized resulted in injection into TiO₂ [TiO₂/Rup>IIIp>鈥揘Ar₃ + h谓 鈫?TiO₂(ep>鈥?/sup>)/Rup>IIIp>鈥揘Ar₃p>鈥?p>] followed by rapid back interfacial electron transfer to another oxidized compound that had not undergone excited-state injection [TiO₂(ep>鈥?/sup>)/Rup>IIIp>鈥揘Ar₃ 鈫?TiO₂/Rup>IIp>鈥揘Ar₃]. The net effect was the photogeneration of equal numbers of fully reduced and fully oxidized compounds. Lateral intermolecular hole hopping (TiO₂/Rup>IIp>鈥揘Ar₃ + TiO₂/Rup>IIIp>鈥揘Ar₃p>鈥?p> 鈫?2TiO₂/Rup>IIIp>鈥揘Ar₃) was observed spectroscopically and was modeled by Monte Carlo simulations that revealed an effective hole hopping rate of (130 ns)p>鈭?p>.